In the recovery of hydrocarbons from underground formations, it is common to fracture the formations with fluids forced down a wellbore under considerable pressure. Various types of fracturing fluids may be used. This invention is concerned with the use of hydrocarbon fracturing fluids, such as kerosene, Diesel oil, and the like. It is common to viscosify or gel hydrocarbon fracturing fluids so they are better able to handle and distribute the propping agents commonly mixed with them. Propping agents such as sand or other relatively hard particulates are used to maintain the fissures in the formation after they are fractured, to assure the recoverable hydrocarbons in the formation are able to flow through the formation to be recovered.
It is desirable that the additives for the fracturing fluid should act rapidly and efficiently to make a useful--that is, a viscous--gel from a small amount of chemical.
Dialkyl orthophosphates, particularly in the form of their aluminum salts, have been used as components of hydrocarbon gelling agents for many years--see the generic description in Monroe's U.S. Pat. No. 3,575,859, for example, issued in 1971. Monroe uses the dialkyl phosphate esters in combination with alkyl and alkanol amines having up to 4 carbon atoms; he also uses certain polyamines. In U.S. Pat. No. 4,153,649, Griffin lists eighteen US patents said to teach the preparation of phosphate esters useful in formation fracturing, incorporates them by reference, and goes on to discuss several others. More recently, McCabe, in U.S. Pat. No. 5,271,464, employs alkyl orthophosphate esters with aluminum and iron compounds to make a gel; he uses them in combination with a monohydric alcohol having from 2 to 4 carbon atoms and an alkyl or alkanol amine having from 8 to 18 carbon atoms. The gel is used as a temporary plugging agent. McCabe also, in European Patent Application 0 551 021 A1, suggests a similar composition as a fracturing agent.
Smith and Persinski (U.S. Pat. No. 5,417,287) suggest iron compounds in combination with orthophosphate esters to make a viscous hydrocarbon fracturing medium, and, in U.S. Pat. No. 5,614,010, include a low molecular weight amine and, optionally, a surfactant.